The purpose of this project is to undertake a systematic study of the interaction of follicle-stimulating-hormone (FSH) with specific receptors in the rat testes. Highly purified human or rat FSH, iodinated under conditions which permit retention of biologic activity, will be utilized as the radioligand in these studies. The properties of the FSH receptor interaction will be investigated by techniques successfully applied in earlier studies on LH-rat testes receptor interactions. Although initial experiments will be concerned with fundamantal properties of specific FSH receptors in homogenates of rat testes tubules, the ultimate goal is to understand the nature of the FSH interaction with receptors in isolated seminiferous tubule membrane preparations, and with receptors after solubilization and purification. Solubilization will be attempted through use of ionic and non-ionic detergents, by freeze-thawing techniques and other methods as seem appropriate. Chemical purification of the receptor will be pursued through use of a variety of methods, but it is hoped that affinity chromatography will allow a rapid advance in this area. The effect of variables such as pH, ionic strength and temperature on the kinetics and other aspects of hormone-receptor interactions will be examined, and then a comparison will be made of properties of receptors in isolated membrane fractions with those obtained after solubilization and purification. The chemical properties of the receptors will be probed through use of chemical and enzymatic modifications. The relationship of hormone binding and activation of the adenyl cyclase system will also be studied. Attempts will be made to develop a radioligand assay for FSH, and this will be utilized in the quantitation of FSH activity in pituitary fractions, in physiologic fluids, and will be applied to structure function studies on FSH. Based on our experiences with the rat system, initial attempts will be made to perform similar studies on FSH receptors in human and monkey testicular tissue. All of the methodologies required to pursue the above program are currently in use in our laboratory and have already been applied to studies on LH- receptor interaction.